Optical information recording media (optical disks) capable of recording information for once using a laser light have conventionally been known. The optical disks are also referred to as write-once CDs (so-called CD-Rs) and, in a typical structure thereof, a recording layer containing an organic dye, a reflection layer containing a metal such as gold and a protective layer made of a resin are laminated successively in this order on a transparent disk-shape substrate. Information is recorded onto the CD-R by irradiating the CD-R with a laser light in a near infrared region (usually, a laser light near 780 nm in wavelength). An irradiated portion of the recording layer absorbs the light to locally increase the temperature at the portion, and the optical characteristics of the portion are changed by physical or chemical change (for example, formation of pits) to record the information. On the other hand, readout (reproduction) of information is also performed by the irradiation of the CD-R with a laser light of the same wavelength as used for recording. Information is reproduced by the detection of the difference in the reflectance between the portion where the optical characteristics of the recording layer altered (recorded portion) and the portion where the optical characteristics did not alter (non-recorded portion).
In recent years, information recording media of higher recording density are being demanded. To meat such a demand, optical disks called writable digital versatile disks (so-called DVD-Rs) have been proposed. The DVD-R has a structure comprising two disks each comprising a transparent disk-like substrate in which guide grooves (pre-grooves) for tracking of laser light to be irradiated are formed with a narrow width (from 0.74 to 0.8 μm) of one-half or less a groove width of CD-Rs, having provided thereon a recording layer comprising a dye, generally a light-reflecting layer on the recording layer and, if necessary, a protective layer, which two disks are adhered to each other with an adhesive with the recording layers disposed at the inside, or a structure wherein the disk described above and a disk-shaped protective substrate of the same shape as that of the disk are adhered to each other with an adhesive with the recording layer at the inside. The recording and reproduction of information on DVD-R are performed by irradiation with a visible laser light (generally a laser light of from 630 nm to 680 nm in wavelength), and it is believed that recording at higher density than with CD-R is possible.
Among the optical disks, there are known those optical disks having a label stuck on the opposite side to the recording side on which musical data or the like are recorded, with the label having printed thereon visible information such as a title of a music composition of music data recorded on the recording side or a tile for discriminating recorded date. Such optical disks are produced by previously printing the tile or the like on a circular label sheet using a printer and sticking the label sheet onto the opposite side of the optical disk to the recording side.
However, in the case of producing an optical disk having a desired visible image such as a title recorded on the opposite side to the recording side as described above, a printer is additionally required in addition to an optical disk drive. Thus, there is required a complicated operation wherein recording on a recording side of an optical disk is performed by using an optical disk drive, the optical disk is removed from the optical disk drive, and a label sheet having been printed by means of a separately prepared printer is stuck thereon.
Therefore, there has been proposed an optical recording medium which permits display by changing contrast between the surface and the background by using a laser marker on the opposite side to the recording side (see JP-A-11-66617). This method permits recording of a desired image on the opposite side to the recording side without separately preparing a printer. However, this method requires use of a high-power gas laser such as a carbonic acid gas laser due to low sensitivity, and a visible image formed by the laser light as described above has such a low contrast that it has an inferior viewability.
On the other hand, if the same laser light source as is employed for recording or reproducing information (digital information) can be used for recording visible information, the visible information can be displayed by using an apparatus a general user uses for recording. Also, in view of saving hardware source of a recording apparatus, it is preferred that a laser light source used for recording or reproducing information (digital information) can commonly be used as a laser light source for recording a visible image.